It's happened slowly, with little fanfare and a lot of sweat, says work sociologist Mary Lindenstein Walshok.

"While America's imagination has been captured by women entering the professional world, they've been making even more dramatic gains," she says, "in the blue-collar work force.

"Despite all the attention paid to women entering fields like science, medicine and law, census data show that it is in jobs such as carpentry and small-appliance repair, auto mechanics, plumbing, electronics and office-machine services that the greatest rates of change seem to be occurring."

Good pay, interesting work and the possibility of setting their own hours, says Walshok, are major reasons for the boom in blue-collar women. "A woman with a couple of kids who wants good pay and flexibility can have it made with a skilled trade like plumbing."

Although women still represent just a small portion (about 18 per cent) of blue-collar workers, "their rate of increase in the skilled trades is impressive," she says. In 1970 almost one-half million women were working in skilled crafts, up from 277,000 in 1960: a rate of increase twice that for women in all occupations. By 1980 that number had risen to roughly 600,000.

But in a society with a "hidden class consciousness," notes Walshok, 39, "blue-collar women are still viewed as social oddities. Despite the disillusionment with formal education, the resurgence of interest in working with one's hands, in being outdoors and in being physically fit, we are surprised when anyone -- much less a woman -- articulates positive feelings about manual labor.

"We tend to ignore the fact that easily half of our workforce are in skilled and semi-skilled jobs. We see a helicopter go down in Iran, yet we don't make the connection between this attitude and our production problems."

Walshok began working with blue-collar women in 1973, when she was asked -- in her capacity as dean of continuing education at the University of California in San Diego -- to evaluate a program designed to train women for blue-collar jobs.

"I'm fascinated by people who take risks," she says. "And a woman who enters a field outside the boundaries of 'woman's work' has to be somewhat of a risk taker, an independent person who can go it alone if necessary and fight the often negative tide of family, public and co-worker opinion."

Walshok followed the lives of about 100 "blue-collar pioneers" over a four-year period, examining their backgrounds, attitudes, experiences, successes and failures. To succeed in this "male frontier" -- she concludes in her book Blue-Collar Women (Anchor Books, 310 pgs., $7.95) -- a woman "must have strong reasons for making such a move, and either compelling needs or a great deal of confidence to back up her decision."

The women who choose blue-collar work "cannot be reduced to a single prototype," she says. "When options that for decades have been closed begin to open up, a rather dazzling array of types of people, from highly varied backgrounds, emerge as the pioneers.

"They are a complicated, articulate and interesting group of women with a breadth and depth of experience and insight far beyond what common-sense stereotypes suggest." Among her profiles (using pseudonyms):

* Maggie Patterson, a 25-year-old single mother who was earning $3.25 an hour after three years as a key-punch operator. When a recruiter came through her office, seeking women for apprenticeships in blue-collar trades, she signed up as an electronics mechanic, starting at $3.14 an hour. After nearly five years she became acting foreman, earning $9.06 an hour.

* Katie Jenkins, who had completed a two-year college art program and was working full time cleaning houses. When a career counselor suggested skilled, blue-collar work, she enrolled in a welding course and now works as welder in a service shop.

* Molly O'Hara, who got a divorce and her first job at age 37. After 13 years of clerical work and when her three children were grown, she applied for a company apprenticeship in drafting. Now the only woman draftsperson in a large facility, she calls herself the "mother-hen" of her 12-person work group.

Women who have succeeded in blue-collar work, says Walshok, share several important characteristics.

"They had a strong sense of autonomy, the ability to go it alone without needing a lot of supportive feedback. Society traditionally doesn't train women to manage their lives without support systems. Only one-fourth were married and only half had children."

Unlike many women entering the work force, "They were not ambivalent about employment. They were money-oriented, and wanted to be paid what they felt they were worth. A lot of them took on major responsibilities when they were very young. They had a strong sense of self-worth, and liked having a sense of control and accomplishment.

"They liked machinery, enjoyed working with tools and solving problems. Many had a lot of early access to 'tooling.' Many had fathers who worked in skilled trades and as children would help them take apart and put together cars, clocks, juke boxes. Most had very strong female role models."

Despite the popular stereotype, says Walshok, "most did not identify themselves with the women's movement. They realized it helped open up the opportunities for them, but that was it. They largely saw the women's movement as middle-class and white."

Women who tried and quit blue-collar jobs, she says, "were often the ones who tried to work on the social problems first. They wanted to be accepted first, then learn the job.

"The ones who made it concentrated on developing their skills. They had the attitude, 'Just teach me how to do my job. When you see what I can do you'll accept me.' "

For women with aspirations in blue-collar work, Walshok suggests:

* "Be an active learner. Women complain, 'They won't teach me,' but in an apprentice system, you've got to ask good questions or you'll never learn."

* "Have thick skin. You can't crumple if no one wants to sit with you at lunch. You can't take ribbing personally. Male apprentices get kidded, too."

* "Be able to differentiate between harmless hassling and real harassment -- when safety is threatened or when you're being kept from doing your job."

* Stand up for yourself. "Face harassers directly, and say, 'I need a job just like you. Back off and don't add to my problems.'"